Staphylococcus aureus is an important pathogen. Both community-associated and hospital-acquired infections with S. aureus have increased in the past 20 years. Infection of host tissues by S. aureus requires a specific group of staphylococcal adhesive proteins with serine-asparate dipeptide repeats (SDRs). Pathogenic staphylococci express several SDR proteins that are heavily glycosylated by two glycosyltransferases, SdgA and SdgB. In this study, the structure of SdgB from S. aureus was determined in apo. The structure of S. aureus SdgB is similar to that of typical glycosyltransferases, despite having an extra ?-sheet domain. Superimposition of the S. aureus SdgB structure with typical glycosyltransferase structures, we found that one of the SO42- binding sites is very similar to that of UDP binding site in typical glycosyltransferases. In addition, we propose some positive residues, such as Arg43, Arg47, Arg73, Lys92, Arg101, Lys118, Arg120, Arg132, Lys134, Arg137 and Arg150 located in the ?-sheet domain serve as important residues responsible for binding with SDR. In summary, the structure of S. aureus SdgB provides an opportunity to investigate the mechanism of SdgB-mediated glycosylation.